sudden speed reduction

My plan offers up to 60 MPS speed. Between Nov 11 and Nov 15, the speed dropped to between 25 and 40 MPS. Until then it was always over 60 and typically 68MPS. All devices register the same basic speed readings. and there is nver more than one device running at a time here. Modem reports good connections. A new community center opened across the street at about the same time. Could it be possible that the community center is putting a drain on the system? What's my next move to be?